1. Field of the Present Invention
The present invention relates to a method and apparatus for recording onto and reproducing from a recording medium which is preferably realized by a digital data recording and reproducing apparatus in which a rotary head such as a DAT (digital audio tape recorder) is used.
2. Description of the Prior Art
In a magnetic tape recording and reproducing apparatus of a helical scanning system provided with a rotary head which is in the typically conventional art, two magnetic heads are mounted in the opposite direction to each other by 180.degree., at the side of a cylindrical rotary drum. A magnetic tape is wound, as to be inclined by an angle .theta.1 to the vertical plane of an axis line of a rotary drum, to the side of this rotary drum for instance with a wrap angle of 90.degree.. The gap between the above two magnetic heads has an azimuth angle of (angle +.alpha.) and another azimuth angle (angle -.alpha.) for the rotary axis line, respectively. Thereby cross talk can be prevented when reproducing using these two magnetic heads. Therefore, a so-called guard track is not needed between tracks formed by these two magnetic heads, and high density recording can be accomplished.
FIG. 1 is a view showing the track pattern of a magnetic tape 41 on which digital data has been recorded by an apparatus like the above-mentioned. When recording and reproducing, the magnetic tape 41 travels in the direction shown with an arrow 2 at the traveling speed Vt and the rotary drum rotates at the rotation speed Vd, thereby causing the magnetic heads of the rotary drum to scan the magnetic tape 41 obliquely. As the traveling speed Vt is sufficiently slowed to the rotary speed Vd, the inclination .theta.2 of the track on the magnetic tape 41 is roughly equivalent to the angle .theta.1 above-mentioned.
On the magnetic tape 41, a track Ai (i=0 to n) is, for example, the magnetic head whose azimuth angle is +.alpha., and the track Bi is for another magnetic head whose azimuth angle is -.alpha., and digital data is recorded on these tracks, respectively. One pair of tracks, Ai and Bi, constitutes a frame Fi and digital data is recorded and reproduced with this frame Fi used as unit. When reproducing digital data, the traveling speed Vt of the magnetic tape 41 is controlled so that the two magnetic heads can scan on the tracks Ai and Bi individually corresponding thereto
When a recording and reproducing apparatus is used as auxiliary memory unit, for instance, of a computer, digital data is recorded on each of the tracks Ai and Bi. Each of these tracks, Ai and Bi, is separated into, for example, a main data area and an auxiliary data area shown with oblique lines in FIG. 1. The digital data is recorded in the main data area, and information pertaining to the details of recording in the main data area is recorded in the auxiliary data area. For example, block numbers described in detail later are recorded in the auxiliary data area of the tracks Ai and Bi. That is, [p-1] and [p] attached to the tracks Ai and Bi in FIG. 1 express the block numbers recorded in the auxiliary data area of the track.
In a computer or like devices, usually digital data is inputted and outputted, using a block format as the unit of information. The volume of information of this block is variable.
When the data volume of one block exceeds the data capacity of a frame in the above-mentioned magnetic tape recording/reproducing apparatus, the digital data of the block is separated into a plurality of frames and can be recorded.
At this time, a block number to distinguish which block of digital data is to be recorded in the main data area and the tracks are recorded in the auxiliary data area. When reproducing, the required digital data is reproduced block by block on the basis of this block number.
When the digital data is inputted into and outputted from external equipment of a computer, etc. on a block-by-block basis, the inputting and outputting operations are asynchronous with the recording and reproducing operation for which the frame Fi is the unit of the recording and reproducing apparatus. For this reason, the recording and reproducing apparatus is provided with buffer memory, thereby causing the input and output with relation to the external equipment to be accomplished by using this buffer memory. Therefore, a buffer memory having more memory capacity than the recording capacity of a block is used.
As illustrated in FIG. 1, the digital data of a plurality of blocks is reproduced one after another in the order of block numbers. When the digital data of the block p is about to be reproduced, the two magnetic heads read out digital data from the tracks A2 and B2 one after another. Thus, when the capacity of the buffer memory becomes full when digital data of the tracks Ak and Bk of the frame Fk, for instance, is stored in the buffer memory, the magnetic tape stops, and the block of digital data stored before the block number p is outputted block by block from the buffer memory to the external equipment. Thereafter, the magnetic tape 41 is wound back a little before proceeding, thereby causing reading-out of digital data to be started again from the next frame Fk+1 of the block number p and to be stored in the buffer memory.
However, as the traveling of the magnetic tape 41 comes to a stop because the available area runs out in the buffer memory of such a recording/reproducing apparatusis occupied, it is impossible well to trace the magnetic heads to the required track Ak+1, for instance, for the frame Fk+1 when re-starting the magnetic tape 41, thereby causing correct read-out movement not to be conducted. In these cases, as only the block number is written in each frame, it is impossible for the recording/reproducing apparatus to judge whether or not digital data is read out from the frame Fk+1 next. There is a possibility of reproducing and outputting digital data which is different from that to be read out at this time. Therefore, such a recording and reproducing apparatus has little reliability.